Sorry about your fish. I know undissolved grains of salt can burn aquatic creatures should they come in contact with their skin but I'm not sure if this killed her.

Yeah I just don't know what else could have done it. I did a 100% water change, and after adding the salt I noticed that when I put her in, she reacted to the water conditions by surfacing for air almost every 5 seconds. It looked like she was having a hard time swimming down, as if she was floating against her own will. I dumped the water, refilled and reconditioned it, but she still had the same reaction. After a trip to walmart, I returned to find her dead...................... Then again I suppose she was never healthy from the start, as she never ate in 12 days, did a "coughing" gesture a few times with nothing coming up, and was always listless. I still can't help but feel responsible, y'know?

sorry to hear that your fish died but my girlfriends betta did the same exact thing yours did. didnt eat for at least two weeks after we got her and never attempted to go for the food and always sat in the same spot. we did everything you did with the water as well with the changing it and everything often but we could never figure out what happened and now our new betta is doing the same thing for some reason. hopefully were able to figure out whats going on :/